The principal aims of the studies are: 1. To determine morphological and histo-cytochemical age changes in the cellular and matrical complement of skeletal tissues in normal animals, and following injury. 2. To develop a better understanding of changes in the cellular proliferative kinetic behavior and repair potentials of aging skeletal cell systems. 3. To determine the role and effect of diurnal rhythms on skeletal cell systems, and the significant changes associated with increasing age. 4. The data collected and knowledge gained from these continuing studies will be combined and evaluated in the light of our previous 18 years of research in this specific area. In addition, the information will serve to broaden our baseline for future skeletal studies devoted to the assessment of the effects of aging on the maintenance, capacity and response of bone and cartilage to pathology, radiation injury, nutritional and hormonal influences, as well as, physical, chemical and bacterial trauma. 5. The Laboratory for Cellular Research, on the basis of the present N.I.H. grant also serves as a training center for research in aging involving graduate, post-graduate students and professional researchers interested in skeletal aging research. One of our major aims is to continue this contribution to the field of Gerontology. In view of these aims, the Laboratory for Cellular Research is fully equipped and prepared using its experienced technical staff to continue such investigations employing a variety of techniques including analytical morphological, autoradiographic and histo-cytochemical methods at both the light microscopic and electron microscopic levels. The major focus of these studies will continue to deal with the basic question, "How do age changes affect the cellular kinetic behavior and cellular potential for structural and functional maintenance during growth, development and repair of skeletal tissues with increasing age?" In addition, success in our original research endeavors makes it now feasible as well as essential to broaden our aims to the quantitative assessment of our reported ultrastructural changes observed concomitantly with increasing age, especially the lipofuscin granules found associated with connective tissues. To this specific point it is our aim to survey connective tissues other than those associated with the skeleton.